1. Field of the Invention
The present invention relates generally to a hydraulic oil supplying apparatus for an automatic transmission. More particularly, the present invention relates to an improvement of a hydraulic oil supplying apparatus of the foregoing type including a drain path by way of which hydraulic oil is drained after it is delivered from an oil pump to a control valve.
2. Statement of the Related Art
A lay-out concept as shown in FIG. 4 wherein a hydraulic pressure control valve 1 for an automatic transmission (not shown) is mounted on the upper portion of a transmission case 4, a discharge port 8 of an oil pump 2 is disposed on the upper side of the oil pump 2 and a suction port of the oil pump 2 is disposed on the lower side of the same so as to allow hydraulic oil to be sucked up from an oil reservoir 3 on the bottom of the transmission case 4 and then delivered to the control valve 1 has been already proposed by a common assignee to the present invention under Japanese Utility Model Application Laying-open No. 4-84778.
In contrast with another conventional lay-out concept wherein a suction port and a discharge port are disposed on the lower side of an oil pump with the result that there arises a malfunction that it is difficult to arrange oil communication paths, by way of which a torque converter, a cooler, a front clutch, a rear clutch or the like are communicated with the oil pump, without any interference with the suction path and the discharge path each having a considerably large cross-sectional area, the first-mentioned lay-out concept assures that the aforementioned paths can considerably easily be arranged in the vicinity of the oil pump.
According to the first-mentioned lay-out concept, it is proposed that a drain path 9 is arranged so as to allow the oil drained from the control valve 1 to be conducted to the suction port 6 of the oil pump 2.
With this lay-out concept, however, if it is attempted that a drain path is arranged on a member having a plurality of communication paths formed thereon without any interference with these communication paths and associated ports concentratively located in the vicinity of the oil pump, there unavoidably arises a necessity that the space occupied by the oil pump as seen in the axial direction is enlarged by a quantity corresponding to the cross-sectional area of the drain path or the drain passage is arranged with dimensions increased in the radial direction. Especially, a converter housing or a transmission case having the oil pump arranged therein is equipped with a bearing for a counter shaft of a transmission mechanism in addition to the oil communication paths and associated ports. Thus, there is a possibility that although the communication paths and associated ports can easily be arranged in the vicinity of the oil pump, the whole automatic transmission is designed to have larger dimensions due to the arrangement of the foregoing bearing without any interference with the communication paths and associated ports. Otherwise, it is imagined that the drain path is formed using a pipe. In this case, however, there arises a problem that the manufacturing cost would be high.